Piston pump

ABSTRACT

A piston pump assembly having a single drive gear assembly associated with two adjacent pump cylinders. Each pump cylinder has a separate valve unit associated therewith. The two pump cylinders have a common piston rod having a pump piston arranged at each end. The piston pod is formed as a toothed rack and the drive gear assembly includes motor-driven gearwheels engaged with the toothed rack.

RELATED APPLICATIONS

This application claims the benefit of the Norwegian application19995084 filed Oct. 18, 1999 and the international applicationPCT/NO00/00341 filed Oct. 17, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a piston pump as disclosed in thepreamble of claim 1.

2. Description of the Related Art

The invention has been especially developed as a drilling fluid pump.The standard drilling fluid pumps are connecting rod operated pistonpumps. These are relatively heavy structures, and their service life isalso comparatively short.

Therefore there is a need for a new type of drilling fluid pump that islighter in weight and has a longer service life.

SUMMARY OF THE INVENTION

This need is met by means of a piston pump as disclosed in claim 1.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional features of the invention are disclosed in the dependentclaims, and advantages of the invention will be explained in detail inthe following description of an exemplary embodiment with reference tothe drawings, wherein

FIG. 1 is a perspective view of a drilling fluid pump according to theinvention;

FIG. 2 is a side view of the pump in FIG. 1;

FIG. 3A, with detail FIG. 3B, is a sectional view taken along a line 3—3in FIG. 2;

FIG. 4 is a sectional view taken along the line 4—4 in FIG. 2;

FIG. 5 is a perspective view of an embodiment in which two pumps areplaced on a frame.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The drilling fluid pump shown in FIG. 1 comprises two valve units 1 and2, two pump cylinders 3 and 4, and a central drive unit 5. The valveunits 1 and 2 are as known from the conventional pumps, and the pumpcylinders 3 and 4 are also conventional. Therefore these components arenot described in any more detail here.

As shown in FIGS. 2 and 3, the central drive unit 5 comprises a housing6 and two electric drive motors 7 and 8 mounted thereon. The two drivemotors 7 and 8 are via gearboxes 9, 10 and gear wheels 11-14drive-connected to a toothed rack 15 which moves in the two pumpcylinders 3, 4 as shown in FIG. 3. At each end, the toothed rack 15 hasa piston 16 and 17 respectively which act as pump pistons in theirrespective cylinders 3, 4. The toothed rack 15 has an H-shapedcross-section, see FIG. 4.

The pump shown in FIG. 1 is symmetric, i.e., the two valve units 1, 2and the pump cylinders 3, 4 are identical to one another.

When the pump is in operation, the toothed rack 15 is moved back andforth by the electric motors 7, 8 via the gearboxes 9, 10 and thegearwheels 13-14. The pistons will then draw in and force out drillingfluid through the associated valve unit 1, 2.

The new drilling fluid pump can be made having a weight that is aboutfour times lighter than the conventional drilling fluid pumps which haveheavy drive gears. The reduction in weight will depend on,the length ofthe cylinders. An expedient pump cylinder length is three meters, whichis about six times longer than in a conventional pump.

The piston velocity can then be the same as in a conventional pump, andthe pump cylinder diameter can be as in the known pumps, for example asmuch as 6″ in cylinder diameter. A service life is thus obtained for theinventive pump that is six times longer than that of the conventionalpumps.

FIG. 5 shows a drilling fluid pump which differs from that in FIG. 1only in that it has been “doubled”, and where the pumps are placed on atransport or support frame 18.

What is claimed is:
 1. A pump unit comprising: a central housing; atleast two separate elongated pump cylinders attached to the centralhousing so as to extend in opposite directions from the central housing;respective pump pistons positioned within the respective pump cylindersand outside of the central housing; a piston rod in the form of atoothed rack having one of the pump pistons attached to each end of thetoothed rack; a central drive unit comprising electric motors drivingrespective gear wheels in engaging interaction with the toothed rack formoving the pump pistons back and forth in the pump cylinders,respectively; and a valve unit at each end of the elongated pumpcylinders remote from the central housing, each of the valve unitscontaining inlet and outlet valves for the pump cylinders.
 2. The pumpunit of claim 1, wherein the central housing and the valve units aremounted on a common transport/support frame.
 3. The pump unit of claim1, wherein the electric motors are reversible so as to drive therespective gear wheels in opposite directions to move the pump pistonsback and forth in the pump cylinders.
 4. The pump unit of claim 1,wherein at least a first electric motor is arranged to drive respectivefirst gear wheels in a first direction and at least a second electricmotor is arranged to drive respective second gear wheels in an oppositedirection so to move the pump pistons back and forth in the pumpcylinders.